# Online Resource 2 — Supplementary Table S1
## Negative-control test of the operational observability signature

Generated by `scripts/13_observability_negative_control.py` from a clean pipeline run.
All field lists and exclusion rules below are fixed in the script **before** any estimate
is formed. Statues, not field x statue observations, are the unit of dependency: the
bootstrap resamples statues within stage and the interaction test clusters on the statue.

### S1.1 Field classification rules

| Class | Rule | Fields |
|---|---|---|
| Candidate (basal) | The five basal fields already used in Section 3.9; inherited from the published analysis, not selected for this test | `BASAL_SURFACE_OUTLINE`, `BASAL_EDGE_1`, `BASE_PROFILE_FRONT_SHAPE`, `BASE_PROFILE_BACK_SHAPE`, `BASE_ANGLE` |
| Matched control | Categorical shape / outline / profile descriptors of non-basal anatomy, matched one-to-one in kind, same survey protocol | `TOP_HEAD_OUTLINE`, `HEAD_PLAN_SHAPE`, `HEAD_PROFILE_SHAPE`, `BODY_PLAN_SHAPE`, `BODY_PRO_SHAPE` |
| Broad control | All non-basal categorical morphological descriptors (29 fields) | see S1.6 |

Deliberate exclusions, with reasons:

| Excluded | Reason |
|---|---|
| `*_PIECES` (fragment counts) | Recording a fragment count and recording the base may share a common cause in documentation intensity; including them would import the co-recording confound the framework warns against |
| `EYE_SOCKETS`, `EYE_PLAN` | The eye sockets are the paper's positive control; reuse here would be circular |
| `GENERAL_CONDITION`, `STATE_FOUND`, `ORIENTATION_UPRIGHT_POSITION` | Taphonomic state, not morphological description |
| `X`, `Y`, `URL_LINK`, `QC`, identifiers, `LOCATION_*`, `MATERIAL_TYPE` | Administrative or geographic, not morphology |

### S1.2 Observability by stage and field class (percent of fields recorded)

| Stage | n statues | Basal (5) | Matched control (5) | Broad control (29) |
|---|---:|---:|---:|---:|
| In-bedrock | 315 | 0.6% | 2.2% | 1.8% |
| Detached | 44 | 12.3% | 48.2% | 44.9% |
| Road | 62 | 39.0% | 48.7% | 32.6% |
| Platform (ahu) | 481 | 23.4% | 26.7% | 20.9% |

### S1.3 Difference in differences, by transition

| Transition | Controls | DiD (pp) | 95% CI (statue bootstrap) | Bootstrap tail |
|---|---|---:|---|---|
| Bedrock to detached | Matched | -34.32 | [-43.15, -24.90] | 2000 of 2000 bootstrap replicates were non-positive; bootstrap lower-tail proportion = 1.0000 |
| Detached to road | Matched | +26.23 | [+15.13, +36.41] | 0 of 2000 bootstrap replicates were non-positive; bootstrap lower-tail proportion < 0.0005 |
| Detached to road | Broad | +39.02 | [+27.01, +49.96] | 0 of 2000 bootstrap replicates were non-positive; bootstrap lower-tail proportion < 0.0005 |

Interaction (stage x field class), statue-clustered: coefficient 0.2623, p = 3.27e-06.

The bedrock-to-detached row is negative: the first transition raises recorded morphology
broadly rather than specifically at the base. Absolute exposure and anatomical specificity
are distinct properties, and only the detached-to-road transition carries the selective
basal signature relevant to the road-platform comparison of Component B.

### S1.4 Leave-one-control-out (detached to road, matched set)

| Control dropped | DiD (pp) |
|---|---:|
| `TOP_HEAD_OUTLINE` | +21.98 |
| `HEAD_PLAN_SHAPE` | +19.61 |
| `HEAD_PROFILE_SHAPE` | +21.72 |
| `BODY_PLAN_SHAPE` | +33.72 |
| `BODY_PRO_SHAPE` | +34.13 |

### S1.5 Each candidate field alone, against the matched control mean

| Basal field | DiD (pp) |
|---|---:|
| `BASAL_SURFACE_OUTLINE` | +22.93 |
| `BASAL_EDGE_1` | +24.25 |
| `BASE_PROFILE_FRONT_SHAPE` | +20.66 |
| `BASE_PROFILE_BACK_SHAPE` | +23.59 |
| `BASE_ANGLE` | +39.72 |

### S1.6 Complete enumeration of control subsets

Every possible five-field control subset of the 29 broad-set fields was
enumerated exactly (118,755 subsets). This is a complete audit of the control
universe, not a sample, so it carries no seed dependence.

| Quantity | Value |
|---|---:|
| Subsets enumerated | 118,755 |
| Subsets with non-positive DiD | 0 |
| Minimum DiD (pp) | +1.38 |
| Median DiD (pp) | +39.09 |
| Maximum DiD (pp) | +73.81 |

Broad-set fields entering the enumeration:

```
  HEAD_PLAN_SYMMETRY
  HEAD_PLAN_SHAPE
  HEAD_PROFILE_SYMMETRY
  HEAD_PROFILE_SHAPE
  TOP_HEAD_OUTLINE
  TOP_HEAD_OUTLINE_SYMMETRY
  TOP_HEAD_SURFACE
  NOSE_PROFIE
  NOSE_PLANVIEW
  NOSTRIL_PLANVIEW
  EAR_LOBE
  EAR_DETAIL
  LIPS_PROFILE
  LIPS_SHAPE
  CHIN_PROFILE
  NOSE_BRIDGE
  PECTORALS
  NECK
  BACKBONE_VERT
  BODY_PLAN_SYMMETRY
  BODY_PLAN_SHAPE
  BODY_PROFILE_SYMMETRY
  BODY_PRO_SHAPE
  BODY_SURFACE_DETAIL
  BODY_FRONT_PROFILE
  BODY_BACK_PROFILE
  BELLY_BUTTON
  HAND_DESIGN
  HEAD_BACK_ALIGNMENT
```

### S1.7 Scope of the claim

The analysis establishes that the structure of observability is selectively anatomical and
associated with operational context. It does not identify which physical or procedural
process produces that selectivity. Exposure, fall position, fragmentation, accessibility and
survey practice all remain candidate mechanisms, and separating them would require data on
documentation effort that is independent of the morphological record itself. No taphonomic
causal claim is made or implied.
